Circuit arrangements for operating a series circuit of a plurality of low-pressure gas-discharge lamps are already known from the prior art. Circuit arrangements such as these have a resonant circuit including a resonant inductor and a resonant capacitor; the resonant capacitor is connected in parallel with the series circuit of the gas-discharge lamps. Furthermore, at least one so-called sequence start capacitor is in general used in this case, which, when two lamps are connected in series, is connected in parallel with one of the two lamps. This makes it possible to reduce the effectively required starting voltage for the series circuit of the lamps since, until the lamp which is not capacitively bridged is started, virtually all of the voltage which is applied across the series circuit is applied to this lamp, which is started before the other lamp. This ensures sequential starting of the lamps (sequence) and the required total starting voltage for this configuration results approximately from the starting voltage plus the burning voltage of one lamp. One disadvantage in this case is the fact that the total voltage across the lamps is in practice also applied to one lamp during the preheating of the lamps. This value must not exceed a maximum value since, otherwise, the lamps would be started before the electrodes have been adequately preheated, and this would have a very negative influence on the ability of the lamps to withstand switching.
In the present case, there is particular interest in the preheating of electrodes of the gas-discharge lamps. It is prior art for additional heating windings to be used on the resonant inductor for this purpose. However, a procedure such as this results on the one hand in not inconsiderable continuous heating power levels in the electrodes, which has a negative influence on the efficiency of the overall system, including the circuit arrangement and the gas-discharge lamps. On the other hand, a plurality of heating windings—in general, three additional heating windings are used when two gas-discharge lamps are connected in series—should be wound, should be guided and should be isolated, and this is complex. In particular, the isolation of a large number of additional heating windings is costly. If special induction fittings are used, which provide separate chambers for isolation of the heating windings, considerably less winding space is available for the main winding of the resonant inductor, and it is necessary to use thinner, and therefore higher-resistance, wire. In general, this results in considerable thermal problems in this component.
It is also known for additional heating circuits to be used for preheating electrodes of gas-discharge lamps. In this context, reference is made to the disclosure in document DE 44 25 859 A1. The circuit arrangement described in this document includes a heating circuit which can be used to preheat the electrodes of two gas-discharge lamps. When two lamps are connected in series, a heating circuit such as this has a separate heating transformer, a bridge rectifier, two transistors (one of which is a power MOSFET that is resistant to the starting voltage), a plurality of diodes, and a multiplicity of non-reactive resistors. A heating circuit such as this makes it possible to ensure adequate preheating of the electrodes of the gas-discharge lamps. However, one particular requirement is to achieve reliable preheating of the electrodes of at least two series-connected gas-discharge lamps without having to use a multiplicity of additional components.